We demonstrate stable and tunable light emission in ultraviolet to near infrared regime by using annealed SiO_x sample. By adjusting the ratio of Si and O of SiO_x, different wavelengths such as ultraviolet, visible and near infrared photoluminescence can be tuned. From the results of transmission electron microscope, various sizes (1~4 nm) of the embedded Si nanoparticles were formed. Nanoparticles with smaller sizes were indeed formed for UV-blue emitting samples and the origin of light emission may be misattributed to the quantum confinement effects. However, we found the efficient and stable light emission in UV-blue regime, with lifetime on the order of nanoseconds, is dominantly from the defects.